Electrolytic processes comprising acid electrolyte baths are employed for a variety of purposes, including the cleaning or decontamination of metals, and metal articles or devices. Cleaning and decontamination by electrolytic means consists of removing a portion of the surface metal having soil or contaminates entrained therein. Surface removal by electrolysis, whether for aesthetic or practical reasons such as cleaning, is sometimes referred to as "electropolishing".
Electrolytic cleaning systems have been found to be effective for decontaminating metals exposed to radio-nuclides comprising plutonium, uranium, radium, cobalt, strontium, and americium. This system is highly effective for such contaminates when baked on, ground in, or otherwise difficult to remove with conventional decontamination procedures. Electropolishing teechniques typically only require a brief period of a few minutes to completely remove most types of surface contaminates.
In a typical system for electrolytic cleaning of contaminated surfaces of metals, the metal piece to be decontaminated serves as the anode in an acid containing electrolytic cell. The passage of electric current through the cell results in the anodic dissolution of the surface portion of the metal piece and, under proper operating conditions, a progressive smoothing of the surface. Any contaminates adhering to the metal surface or entrapped within surface pores or imperfections are removed along with the surface portion of the metal piece and released into the electrolyte by the metal dissolution process. The amount of metal removed from the surface of the piece to achieve decontamination is usually less than about 0.002 inch, and it is removed uniformly with no preferential attack of grain boundaries or other microstructural aspects. Moreover, the remaining surface after electropolishing has been found to usually have better corrosion resistance and other properties than did the original surface.
The use of electropolishing measures for the removal of radioactive contaminates from metal objects can provide significant savings and other benefits. For instance contaminated machine parts and apparatus can be decontaminated to background radiation levels and then released unconditionally for repair or other service. Metals in general, and articles thereof, can be decontaminated and sold for reuse, salvage or scrap.
Electropolish decontamination, however, produces spent electrolyte comprising an acid such as phosphoric which is contaminated with one or more soluble metal compounds. Typical soluble wastes derived from electrolytically treating high iron or high nickel containing alloys can include a variety of metals such as iron, nickel, molybdenum, copper, zinc, chromium, aluminum, cobalt and manganese. Additionally, when treating radioactive contaminated metals, the spent electrolyte can also include soluble compounds of uranium, plutonium, radium, cobalt, strontium, and americium. The disposal of any radioactive waste material of course requires special considerations which can be more easily complied with if the material is reduced in volume to a maximum degree for safe packaging, transportation and storage.